The known rekeyable lock cylinder, such as disclosed in U.S. Pat. No. 6,860,131 and No. 20090277240, requires that a new authorized key must be pushed into the position (i.e. completely pushed-in) before turning during rekeying process. However, the user generally turns a new authorized key without pushing in it at the position for the known rekeyable lock cylinder structure when rekeying, which has not completed entire rekeying process resulting in that even the next user pushes a new authorized key in at the position (i.e. completely pushed-in), the lock cylinder cannot be unlocked normally. Therefore, how to assure the user pushes a new authorized key in at the position (i.e. completely pushed-in) before performing rekeying operation is an extremely important topic toward the structural design of rekeyable lock cylinder.